The pleura is a membrane which surrounds the lungs and has a two-layer structure including an outer or parietal pleura that is normally attached to the chest wall and an inner or visceral pleura that covers the lungs and adjoining structures. The space between the inner and outer pleurae is referred to as the pleural cavity, pleural space, or intrapleural space.
For ease of illustration, reference is made to the appended FIGURE which is a simplified diagram showing pleural cavity 1, visceral pleura 2, and parietal pleura 3 in relation to lungs 4 and intercostal muscle 5 of an example human (adapted from OpenStax College. “Anatomy & Physiology.” Connexions. Jun. 19, 2013.).
In healthy patients a small amount of pleural fluid, typically a few milliliters, is usually present in the pleural cavity. This fluid is normally produced and reabsorbed continuously such that no considerable accumulation of fluid occurs in the pleural cavity. Certain pathological conditions can lead to an increase in pleural fluid production and/or a decrease in fluid absorption, resulting in a significant accumulation of excess fluid in the pleural cavity. Blood, pus, and/or other bodily fluids may also accumulate in the pleural cavity under certain conditions. This pathologic collection of fluid in the pleural cavity is known as a pleural effusion.
Pleural effusions may be caused by a number of medical conditions including, for example, congestive heart failure, infections, pneumonia, pulmonary embolism, and cancers. Malignant pleural effusions refer to a type of pleural effusion in which the excess accumulation of fluid in the pleural cavity is specifically caused by cancer. Malignant pleural effusions may be caused, for example, by lung cancer, breast cancer, lymphoma, and pleural mesothelioma.
Pleural effusions, including malignant pleural effusions, can impair normal breathing by significantly limiting the expansion of the lungs. In some cases the excess fluid accumulation in the pleural cavity compresses the lungs resulting in breathlessness and/or lung collapse. For some patients, treating the underlying cause of the pleural effusions (e.g., treating the cancer causing a malignant pleural effusion) may be sufficient to mitigate the pleural effusion. Other treatments for pleural effusions include aspiration of the excess fluid or insertion of a chest tube (e.g., thoracic cather, tube thoracostomy, or intercostal drain) into the pleural cavity of the patient to drain the excess fluid. While aspiration or drainage may provide immediate relief for the patient, fluid accumulation and symptoms may reappear such that repeated aspirations or continuous drainage is required.
Pleurodesis, a procedure in which the pleural cavity is treated in an attempt to reduce or eliminate the potential pleural space, may be used to treat patients suffering from recurrent pleural effusions by reducing or obliterating the potential space in which fluid may accumulate. Pleurodesis typically involves fusing together the outer and inner pleurae and may be carried out using surgical and/or chemical means. Examples of typical procedures for pleurodesis are described in Vaz et al., “Pleurodesis: technique and indications,” J Bras Pneumol. 2006; 32(4):347-56, which is incorporated herein by reference in its entirety. Fusion of the inner and outer pleurae may be accomplished, for example, by triggering fibrosis or the formation scar tissue between the inner and outer pleurae to cause the pleural layers to fuse together. Surgical pleurodesis may include, for example, mechanically irritating the pleura and causing the layers of the pleura to scar together. This procedure can be performed, for instance, by scraping the outer pleura with a rough pad (e.g., via thoracotomy). In chemical pleurodesis, a chemical agent which causes inflammation for inducing fibrosis between the inner and outer pleura, for example, may be introduced into the pleural cavity (e.g., via a catheter or chest drain) to fuse the inner and outer pleurae together. Certain chemical agents and procedures that may be suitable for pleurodesis are described in U.S. Pat. No. 6,103,695, which is incorporated herein by reference in its entirety.
Chemical pleurodesis is sometimes preferred over surgical pleurodesis since chemical pleurodesis may be less invasive. However, treatment success can be suboptimal as substantial or adequate reduction of the pleural cavity can be difficult to achieve in some circumstances when the chemical agent is not effectively distributed throughout the pleural cavity of the patient. When portions of the pleura are not sufficiently exposed to the chemical agent, incomplete fusion of the pleural layers may occur. For example, because the chemical agent used in chemical pleurodesis is typically introduced in a liquid or slurry, the chemical agent may collect at certain locations in the pleural cavity due to gravity, possibly resulting in an uneven distribution of the chemical agent. In some cases the chemical agent may not maintain contact with portions of the pleura for a sufficient amount of time to trigger fibrosis because, for example, the liquid or slurry drains to lower regions of the pleural cavity.